1. Field of the Invention
The present invention relates to a personal watercraft (PWC) and an engine mounted in the personal watercraft. More particularly, the present invention relates to a jet-propulsion personal watercraft which ejects water pressurized and accelerated by a water jet pump rearward and planes on a water surface as the resulting reaction, and an engine mounted in a body of the watercraft.
2. Description of the Related Art
In recent years, so-called jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. The personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a hull bottom surface and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.
In the personal watercraft, an engine for driving the water jet pump is contained in an engine room inside a body constituted by a deck and a hull. The body is provided with an opening such as an air inlet for feeding fresh air to the engine inside the engine room. Therefore, during cruising of the watercraft, water outside the watercraft enters the engine room through the opening.
Recently, the use of a four-cycle engine in the personal watercraft has been contemplated. In some four-cycle engines, an ignition plug is attached to a top portion of a cylinder of the engine so as to extend toward a center of the cylinder. For the purpose of attaching the ignition plug, the top portion of the engine, i.e., a cylinder head and a cylinder head cover, is provided with a concave portion that opens upwardly to accommodate the ignition plug. In the engine having such a structure, the water entering the engine room might flow into the concave portion. While the concave portion provided in the top portion of the engine is located at a high position, water splashed by a rotating member inside the engine room, such as a rotating coupling or propeller shaft, might fly into the concave portion.